The present invention relates generally to a motor having a rotor with interior permanent magnets, more particularly it relates to a motor with interior split-permanent-magnets, such that it restrains eddy-currents from occurring and prevents demagnetization of the magnets.
FIG. 11 illustrates a rotor with interior permanent magnets of a conventional motor. The motor has rotor 310 in which permanent magnets 312 are embedded, and rotor 310 is disposed in a stator (not shown) with concentrated windings, so that the motor can be driven by not only magnet torque but also reluctance torque. This rotor is hereinafter referred to as a xe2x80x9crotor with interior permanent magnetsxe2x80x9d.
However this conventional motor has the following problems:
Compared with a motor with a distributed-winding stator, a motor with a concentrated-wound stator subjects itself to greater changes of magnetic flux interlinked with rotor 310 when the motor rotates. As a result, a large eddy-current occurs in magnets 312 embedded in the rotor, and thus the motor with a concentrated-wound stator is vulnerable to irreversible demagnetization of the magnets Meanwhile, the distributed-winding stator is structured in the following way: A slot is formed between two stator-teeth, and a plurality of teeth thus form a plurality of slots. Windings striding over at least one slot are provided, and part of a winding of a phase exists between pitches of another phase winding. The concentrated-winding stator, on the other hand, is structured by providing a winding of one phase to one stator tooth respectively.
The reason why the motor having the concentrated-winding stator is vulnerable to demagnetization is detailed hereinafter.
It is well known that eddy current loss xe2x80x9cWexe2x80x9d is proportionate to a square of maximum operable magnetic-flux-density xe2x80x9cBmxe2x80x9d, and this relation can be expressed in the following equation.
We=Pt/t={1/(6xcfx81)}xcfx802f2Bm2t2[W/m3]
where
Pt=power consumption
t=plate width interlinking with the magnetic flux
xcfx81=resisting value proper to the permanent magnet
f=exciting frequency
Since the motor having the concentrated-winding stator is subjected to greater changes in magnetic flux running through the rotor, the maximum operable magnetic-flux-density xe2x80x9cBmxe2x80x9d in the above equation becomes greater and thus eddy-current-loss xe2x80x9cWexe2x80x9d grows larger.
If a motor has the concentrated winding stator, and yet, the permanent magnets are stuck onto an outer wall of the rotor, the changes in magnetic-flux-density is not so large that the demagnetization of the magnets due to the eddy-current-loss is negligible. In the motor having the concentrated winding stator and a rotor in which the permanent magnets are embedded, the space between the magnet and the outer circumference of rotor core 314 forms a path for the magnetic-flux to flow. The density of magnetic-flux from the stator changes depending on the position of stator teeth with regard to the magnets, so that magnitude of changes in the magnetic-flux-density at the path is increased. As a result, eddy-current occurs in magnets 312 embedded in rotor 310, thereby heating the magnet to produce irreversible demagnetization of the magnet.
The present invention addresses the problems discussed above and aims to provide a motor having a rotor with interior-permanent-magnets. This rotor produces less eddy-current and can prevent demagnetization in the permanent magnets embedded in the rotor.
The motor of the present invention comprises the following elements:
a rotor in which permanent magnets are embedded, and
a stator of which teeth are wound by windings in a concentrated manner.
The permanent magnets are split into magnet pieces, and insulating sections are inserted into respective gaps between respective magnet pieces. This structure splits the magnet electrically, thereby restraining the eddy-current from occurring and then suppressing the heat-demagnetization the magnets embedded into the rotor.